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Molecular switches. Samples of chemicals which act as molecular switches being bathed in ultraviolet light. This light alters the molecular structure of the compound by closing a bond between two thiophen (carbon-sulphur) rings. This allows the electrons of the molecule to roam over the entire structure, and the molecule will conduct a current. When bathed in infrared light, the new bond is broken and the electrons become localised - preventing the passage of a current. This switching 'on' and 'off' could be exploited in future optical computers, in which the chemicals would form molecule-sized switches.